Add game end status with an end_game DM tool and automatic 0-HP detection

Games now have a status/ended_reason pair. The DM can call the new
end_game tool when the story reaches a real conclusion (victory,
defeat, or a resolved one-shot), and the backend independently ends
the game whenever a character's HP drops to 0 or below, regardless of
whether the DM narrates it. The frontend shows a banner and a
"Beendet" badge once a game ends.

HP moves from the freeform combat_stats bag into dedicated
current_hp/max_hp columns on Character, since reliably detecting 0 HP
requires a real integer rather than parsing strings like "3/10" out of
an LLM-authored key/value dict. Also fixed combat_stats to fully
replace on each upsert instead of merging, matching its documented
contract — the merge was leaving stale keys (old HP/TP text) behind
after the model stopped sending them.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/app/llm/orchestrator.py

@@ -9,7 +9,7 @@ from app.config import settings
 from app.llm.client import get_dm_system_prompt, get_llm_client
 from app.llm.context import build_context
 from app.llm.json_utils import fix_double_escaped_unicode
-from app.llm.tools import character_sheet, dice
+from app.llm.tools import character_sheet, dice, end_game
 from app.models.game import Game
 from app.models.message import Message
 from app.rag.retrieval import build_rag_block
@@ -22,6 +22,7 @@ MAX_TOKENS = 4096
 TOOLS = [
     {"type": "function", "function": dice.TOOL_SCHEMA},
     {"type": "function", "function": character_sheet.TOOL_SCHEMA},
+    {"type": "function", "function": end_game.TOOL_SCHEMA},
 ]
 
 
@@ -35,6 +36,8 @@ async def _execute_tool_call(
             return dice.roll(tool_input["notation"])
         if tool_name == "upsert_character_sheet":
             return await character_sheet.upsert(session, game_id, tool_input)
+        if tool_name == "end_game":
+            return await end_game.end(session, game_id, tool_input)
         return {"error": f"Unknown tool {tool_name!r}"}
     except Exception as exc:  # noqa: BLE001
         logger.warning("Tool call %s failed: %s", tool_name, exc)
@@ -42,11 +45,30 @@ async def _execute_tool_call(
         return {"error": str(exc)}
 
 
+async def _check_hp_game_over(session: AsyncSession, game_id: uuid.UUID, result: dict) -> str | None:
+    """After an upsert_character_sheet call, auto-ends the game if the character it touched
+    dropped to 0 HP or below. Returns the end reason if the game was just ended, else None."""
+    current_hp = result.get("current_hp")
+    if current_hp is None or current_hp > 0:
+        return None
+
+    game = await session.get(Game, game_id)
+    if game is None or game.status == "ended":
+        return None
+
+    reason = f"{result.get('name', 'Ein Charakter')} ist bei {current_hp} Trefferpunkten zusammengebrochen."
+    game.status = "ended"
+    game.ended_reason = reason
+    await session.commit()
+    return reason
+
+
 async def run_dm_turn(
     session: AsyncSession,
     game_id: uuid.UUID,
     latest_player_message: str | None = None,
     on_roll: Callable[[str], Awaitable[None]] | None = None,
+    on_game_ended: Callable[[str], Awaitable[None]] | None = None,
 ) -> Message:
     client = get_llm_client()
     system_prompt = get_dm_system_prompt()
@@ -90,6 +112,17 @@ async def run_dm_turn(
             if tool_call.function.name == "roll_dice" and on_roll is not None:
                 await on_roll(tool_input.get("notation", ""))
             result = await _execute_tool_call(session, game_id, tool_call.function.name, tool_input)
+
+            end_reason = None
+            if tool_call.function.name == "end_game" and "reason" in result:
+                end_reason = result["reason"]
+            elif tool_call.function.name == "upsert_character_sheet":
+                end_reason = await _check_hp_game_over(session, game_id, result)
+                if end_reason:
+                    result = {**result, "game_ended": True, "end_reason": end_reason}
+            if end_reason and on_game_ended is not None:
+                await on_game_ended(end_reason)
+
             messages.append(
                 {
                     "role": "tool",